Resistance locking mechanism

ABSTRACT

A resistance locking mechanism having a work contacting push rod for holding a work piece against movement so that the work piece can be removed and reinserted without movement of the push rod. A strong force holds the push rod against movement while the push rod bears against the work piece with a moderate force. A housing has a bore in which a plunger slides between a locked and unlocked position. The push rod slides within the plunger with means biasing the push rod outwardly with respect to the plunger. A locking element having wedging fingers is carried by the push rod and is wedged against the push rod for locking the same at the front end of the housing when the plunger moves into the locked position.

[111 3,799,533 [451 Mar. 26, 1974 RESISTANCE LOCKING MECHANISM [76] lnventor: Richard C. Malott, 321 N. Jackson,

Spring Lake, Mich. 49456 [22] Filed: Oct. 18, 1971 [21] Appl. No.: 190,186

[52] US. Cl 269/32, 269/90, 269/188, 269/201, 269/203, 269/228, 279/51 [51] Int. Cl B23q 3/08, B25b 1/02, B25b l/l4 [58] Field of Search, 269/20, 32, 35, 90, 188, 269/201, 203, 228; 279/41, 51

[56] References Cited UNITED STATES PATENTS 2,568,393 9/1951 Helbig 269/203 X 2,664,015 12/1953 Moore 269/90 X 3,584,351 6/1971 Sliwinski 269/49 UX 1,871,463 8/1932 Olson .Q 279/51 X 3,444,783 5/1969 Fredd 91/44 X 469,325 2/1892 Bowers et a1. 279/51 UX 3,171,663 3/1965 Stark 279/51 X 2,308,099 1/1943 ObeCl'ly... 269/35 X 3,192,600 7/1965 Jones 269/229 X 3,237,463 3/1966 McPherson 269/228 X 1,910,121 5/1933 Muntz 279/56 X Primary Examiner-Othell M. Simpson Assistant Examiner-Joseph T. Zatarga Attorney, Agent, or Firm-McGar1-y and Waters [5 7] ABSTRACT A resistance locking mechanism having a work contacting push rod for holding a work piece against movement so that the work piece can be removed and reinserted without movement of the push rod. A strong force holds the push rod against movement while the push rod bears against the work piece with a moderate force. A housing has a bore in which a plunger slides between a locked and unlocked position. The push rod slides within. the plunger with means biasing the push rod outwardly with respect to theplunger. A locking element having wedging fingers is carried by the push rod and is wedged against the push rod for locking the same at the front end of the housing when the plunger moves into the locked position.

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FIG. 7 45 45 1 RESISTANCE LOCKING MECHANISM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to resistance locking mechanisms, In one of its aspects, the invention relates to a mechanism for releasably holding a work object in a fixed position, the work contacting member being set in position upon contact with the work and held firmly against movementin the work contacting position so that the object can be removed and replaced with another similar work piece if desired.

2. BACKGROUND OF THE INVENTION Resistance locking mechanisms are used for holding and retaining work pieces against movement. A locking mechanism has a work contacting push rod which extends from a cylinder body to contact the work and is thereafter automatically locked in place. The push rod thus firmly holds the work against movement, but in addition, is locked in place so that the work piece may be removed and replaced by another similar work piece without readjustmentof the push rod.

Heretofore, most of such resistance locking mechanisms have been fluidoperated in the sense that fluid pressure is required to actuate the locking mechanism. Furthermore, such cylinders have required expensive and complicated locking mechanisms. Examples of such cylindersv are disclosed in the US. Pat. Nos. 2,988,058, to Warnecke, 3,429,233 Wright, and 3,444,783 Fredd.

In my copending application Ser. No.1 1,213, filed Feb. 13, 1970, there is disclosed and claimed a fluid operated resistance locking cylinder of simple construction, yet the cylinder is very effective in operation. While this cylinder is effective in fluid control systems, a need exists for a simple mechanical locking mechanism for non-fluid systems.

BRIEF STATEMENT OF THE INVENTION Accordingto the invention, there has now been devised a simplified, yet effective, mechanical resistance locking mechanism in which a push rod is firmly locked by mechanical means in a selected position upon meeting resistance from a work piece. The locking mechanism has a housing with an axial bore extending therethrough. The housing has tapered surfaces at one end openinginto the housing bore. A plunger is mounted for reciprocal movement within the bore between a locked and unlocked position. A push rod extends through the opening in the one end of the housing and is mounted for reciprocal movement with respect to the plunger with means biasing the push rod outwardly with respect to the plunger. A locking member is carried by the push rod within the bore of the housing and is axially slidable with respect to the housing bore and push rod. The locking member has resilient locking members for mating with the conical recess in the housing and clamping the push rod. Means bias the locking member toward the conical recess with respect to the plunger. Means are further provided for selectively moving the plunger axially within the bore between the locked and unlocked positions so that movement of the plunger from the unlocked position to the locked position first extends the push rod outwardly until resistance is met and then moves the locking member into locking engagement with the tapered recess about the push rod.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described with reference to the accompanying drawings in which:

FIG. I is a sectional view through a mechanical resistance locking mechanism according to one embodiment of this invention.

FIG. 2 is a sectional view similar to FIG. 1 illustrating the push rod in a work contacting position.

. FIG. 3 is a sectional view similar to FIG. 2 illustrating the locking mechanism in final locked position.

FIG. 4 is a partial sectional view along 4-4 of FIG. 3.

FIG. 5 is a sectional view similar to FIG. 3 illustrating the range in which the push rod is operative and an optional thrust unit.

FIG. 6 is a side elevational view, partly in section, and similar to FIG. 1 illustrating another embodiment of the invention with the mechanism in the unlocked position.

FIG. 7 is a top plan view, reducedin size, of the embodiment illustrated in FIG. 6 and illustrating the locking mechanism in the unlocked position.

FIG. 8 is a reduced side view of the embodiment of FIG. 6 illustrating a first step in the operation of the locking mechanism.

FIG. 9 is a reduced side view similar to FIG. 7 illustrating the locking mechanism in the final locked position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and to FIG. I through 4 in particular, there is shown a side view of a resistance locking mechanism 9 with a thrust device 24, such as a fluid cylinder, and back plate 13 all of which are attached to base 14 through suitable means (not shown). A work piece 29 is loosely placed on base plate 14.

The resistance locking mechanism 9 has at one end a closure plate 12 having bore 15 extending therethrough and terminating in a conical recess 16. Closure plate 12 is attached with screws 10 (FIG. 4) to a block 17 having a bore 18 of a size equal to the wide diameter of the conical recess 16. A cylindrical plunger 19 is connected at its closed end 30 to a piston rod 25 from thrust device 24 by threaded connection 26 and slides axially in bore 18. The piston rod is reciprocally moved by the thrust device for axial movement of the plunger 19. Cylindrical plunger 19 has a bore 20 with closed end 30 and an elongated slot 32 at a bottom portion thereof. A push rod 21 is mounted for axial movement in the bore 20 of plunger 19 and in the bore 15 of plate 12. A spring 22 is mounted within the closed end of the bore 20 and biases the push rod 21 outwardly with respect to the plunger 19. The push rod 21 has a pin 33 extending downwardly therefrom and projecting into slot 32 in the plunger 19. The movement of the push separate resilient wedge members 27 have inclined surfaces 28 extending forwardly about the push rod 21 from the body of the locking member 23. The inclined surfaces 28 mate with the conical recess 16 to force wedge members 27 against push rod 21 when locking member 23 is in the locked position illustrated in FIG. 3. A spring 31positioned between the plunger 19 and the locking member 23 biases the locking member 23 forward with respect to the plunger 19.

In operation, a work piece 29 is placed loosely against a back plate 13 while the push rod 21 and the plunger 19 are in the unlocked position illustrated in FIG. 1. The fluid cylinder is activated to move the plunger 19 and push rod 21 forward until plate 11 on push rod 21 makes contact with work piece 29 as illustrated in FIG. 2. The push rod 21 stops its forward movement but plunger 19 and locking member 23 continue to move in bore 20 until the locking member 23 reaches the conical recess 16. During this movement, spring 22 is compressed within the bore 20 of plunger 19 by rod 21. The locking member 23 stops with the inclined outer surfaces 28 in contact with the conical recess 16. Cylindrical plunger 19 continues to move forward, compressing spring 31 and, consequently, forcing inclined outer surface 28 of locking device 23 against conical recess 16 as illustrated in FIG. 3. This force from spring 31 is transferred to the wedging member 27 which bears down on the push rod 21 to firmly clamp the push rod in place. Thus, rod 21 is caused to be locked in place with respect to the block 17 with the end of push rod 21 firmly in contact with the work piece 24. The push rod is held tightly by the force of the larger spring 31 after locking whereas before locking it was held by the relatively lighter pressure applied by the lighter spring 22.

A toggle clamp is illustrated as a thrust device in FIG. 5. Spring 31 is essential for thrust devices suchas toggle clamps which have a predetermined range of movement. The forward point of movement of the plunger 19 is therefore fixed with respect to the end plate 15. The compression of spring 31 insured locking of lock ing member 23 and eliminates the need for precise adjustment of the thrust devoce to force the plunger 19 to the exact locking point. In contrast, a fluid cylinder would push until resistance stopped it and has a variable stroke. Thus spring 31 would not be necessary using a fluid cylinder as a thrust device.

The size of the work piece held by the resistance locking mechanism can vary greatly. The range of work pieces which can be conveniently held by the mechanism is illustrated in FIG. 5. A large work piece 29 is illustrated by solid lines and the position of the plunger 19, push rod 21 and spring 22 are illustrated for the large work piece. A smaller work piece and the positions of the outer portion of the push rod are illustrated by phantom lines. In both cases, the position of the locking member 23 and the spring 31 would be the same. In each case, the plunger 19 and the locking member 23 are movable between an unlocked position, illustrated in FIG. 1, and a locked position illustrated in FIG. 3. The position of the push rod with respect to the plunger 19 and block 17 will vary with the extent of movement controlled by the size of work piece or by pin 33 in slot 32.

Referring now to FIGS. 6 through 9, a resistance locking mechanism 35 has a main body 41 with an outer cylindrical surface 37 which is placed in bore 38 of mounting plate 36. The forward end of the surface 36 has threads 40 which engage nuts 39. A shoulder 42 at the back end of the cylindrical surface engages the plate 36. Linkage 43 is part of thrust mechanism 51. The thrust mechanism 51 has a handle 52 supported by a linkage 47. A linkage 43 is pivotably mounted at one end by a pin 45 to a rear surface 44 of the body 41 and at the other end to the handle linkage 47 through pin 46. Handle linkage 47 is attached through pin 49 to surface 48 ofa plunger 19. Each side of the thrust mechanism 51 is identical except that one side forms a mirror image of the other. The handle linkage 47 and the link age 43 provides a toggle clamp for the plunger 19 for the locked and unlocked positions. Note that the pivotable connections of the links 43 and the handle link 47 all lie in the same horizontal plane when the plunger 19 is in the locked and unlocked positions. The plunger and locking mechanism of this embodiment are otherwise identical to the embodiment of FIGS. 1 through 9. Consequently, the same numbers have been used to describe corresponding parts. The push rod 21 slides within the locking member 23 and also within the plunger 19 in a manner identical with the embodiment illustrated in FIGS. 1 through 5.

In operation, the clamping assembly will initially be in a retracted position as in FIG. 6 with the handle of the thrust mechanism 51 in a down position. Inward working of the locking mechanism is similar to that of FIGS. 1 through 3. As handle 52 is moved in a counter clockwise direction as viewed in FIG. 6, the handle linkage 47 pivots about pivot pin 46 and causes forward movement of plunger 19 and push rod 21 until contact is made with the work piece 29 as illustrated in FIG. 8. Continued movement of handle 52 in a counter clockwise direction causes handle linkage 47 to move the locking member 23 into locked position, as illustrated in FIG. 9. The position of the locking member 23 is the same as in FIG. 3 wherein the rod 21 is firmly locked in position but at the same time, asserting a lesser force against work piece 29. The degree of force asserted against thework piece 29 can be chosen. by appropri ate selection of the spring 22. The spring force can vary from a very strong force to slight contact.

In the drawings, the push rod 21 is shown biased toward the plate 12 and outwardly with respect to the plunger 19 by a spring 22 with the axial bore 20. In some instances, it may be desirable to provide a very strong biasing force on the push rod 21. To this end the spring 22 can be replaced by the larger spring which is wound around the plunger. In such instance, the bore 18 in the block 17 and the diameter of the plunger 19 will need to be adjusted to accomodate the larger spring which can be seated against the back part of the plunger. The front of the spring can engage pins like pin 33 which are fixed to the inner end of push rod 21 and extend through slots in the plunger 21.

The handle actuating embodiment illustrated in FIGS. 5 through 9 provides a simple hand actuation system when a toggle action locks the plunger in the work engaging position. Thus, when the handle is in the up position as illustrated in FIG. 9, it is toggled into place and will not release the plunger 19' until moved in a clockwise direction by the operation.

The toggle mechanism illustrated in FIG. 5 is similar in construction and operation to the mechanism illustrated in FIGS. 6 through 9. Like numerals have been used to designate like parts. In FIG. 5, the closed end 30 of the plunger 19 threadably engages one end of a connecting rod 57 which slides in an opening in a support plate 55. The base 14 securely holds the support plate 55 in place. A pair of flanges 56 are fixed to the plate 55 and pivotably mount linkage 43 through pin 45. The other end of link 43 is pivotably mounted on handle link 47 through pin 46. The back end of connecting rod 57 pivotably mounts handle link 47 through pins 49. The link 43 is partially broken away in FIG. 5 to show the pin 49 connecting the end of rod 57 and handle link 47.

Reasonable variation and modification are possible within the scope of the foregoing disclosure, the drawings, and the appended claims without departing from the spirit of the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

l. A mechanical resistance locking mechanismcomprising:

a housing having an axial housing bore extending therethrough, said housing bore having a push rod opening at one end of the housing and a plunger opening at the other end of the housing;

a plunger mounted for reciprocal movement within said housing bore, said plunger having an inner end inside the housing bore and an outer end outside the housing bore, with the plunger extending into the housing bore through said plunger opening;

a push rod mounted for reciprocal movement with respect to said housing bore, said push rod having an inner end inside the housing bore and an outer end outside the housing bore, with the push rod extending into the housing bore through said push rod opening, said push rod further having a work contacting member on the outer end thereof;

first resilient biasing means interconnecting the push rod and the plunger, said first resilient biasing means being adapted to resiliently urge the push rod to move outwardly from the housing bore through said push rod opening as the plunger is moved toward said push rod opening;

a locking member carried by said .push rod within said bore of said housing and axially slidable with respect to said housing bore and said push rod, said locking member being positioned for movable engagement with the plunger as the plunger moves toward said push rod opening, said locking member having locking fingers mounted thereon, which are radially movable with respect to said push rod from an unlocked position, wherein the locking fingers are disengaged from the push rod, to a locked position, wherein the locking fingers engage the push rod and prevent axial movement of the locking I member along the push rod;

wedging means adapted to move the locking fingers from their unlocked to their locked positions when the locking member reaches a predetermined point in the housing bore as it is moved toward said push rod opening; and

means for selectively reciprocating the plunger along the housing bore from an unlocked position, wherein the locking fingers are in their unlocked positions, to a locked position wherein the locking fingers are in their locked positions. a

2. A mechanical resistance locking mechanism according to claim 1 and further comprising means for limiting movement of said push rod with respect to said plunger.

3. A mechanical resistance locking mechanism according to claim 1 wherein said plunger moving means comprises a fluid cylinder having a piston rod fixed to the outer end of said plunger.

4. A mechanical resistance locking mechanism ac-' cording to claim 1 wherein movable engagement between the locking member and the plunger is effected by a second resilient biasing means interposed between the locking member and the plunger, said second resilient biasing means being adapted to resiliently urge the locking member toward said push. rod opening as the plunger moves toward said push rod opening.

5. A mechanical resistance locking mechanism according to claim 1 wherein:

the inner end of the plunger has an axial bore therein that extends from said inner end to a closed end inside the plunger;

the inner end of the push rod reciprocally fits within said axial bore; and

said first resilient biasing means comprises a compression spring positioned in the axial bore between the push rod and the closed end of the axial bore.

6. A mechanical resistance locking mechanism according to claim 5 and further comprising means for limiting the movement of said push rod with respect to said plunger.

7. A mechanical resistance locking mechanism according to claim 6 wherein said limiting means com prises an axial slot in said plunger and a pin fixed to said push rod and extending into said slot.

8. A mechanical resistance locking mechanism according to claim 1 wherein said plunger moving means comprises toggle clamp means including a handle for moving said plunger from said unlocked position to said locked position.

9. A mechanical resistance locking mechanism according to claim 8 wherein movable engagement be tween the locking member and the plunger is effected by a second resilient biasing means interposed between the locking member and the plunger, said second resilient biasing means adapted to resiliently urge the locking member toward said push rod opening as the plunger moves towards said push rod opening.

110. A mechanical resistance locking mechanism ac cording to claim 8 wherein said toggle clamp means comprises a handle link pivotably mounted to an outer end of said plunger, and a connecting link pivotably mounted at one end to said housing and at the other end to said handle link.

11. A mechanical resistance locking mechanism according to claim 10 wherein the pivotable mountings of said connecting link and said handle link are aligned in a common plane when in locked and unlocked position.

12. A mechanical resistance locking mechanism comprising:

a housing having an axial housing bore extending therethrough, said housing bore having a push rod opening at one end of the housing and a plunger opening at the other end of the housing;

a cylindrical plunger mounted for reciprocal movement within said housing bore, said plunger having an inner end inside the housing bore and an outer end outside the housing bore, said inner end having an axial bore therein that extends from said inner end to a closed end inside the plunger;

a push rod extending from an inner end inside the housing bore through said push rod opening to a work contacting member on an outer end thereof, the inner end of said push rod extending into the axial bore in the plunger and being reciprocally movable with respect to aid housing bore and said plunger;

a first compression spring means interposed between the inner end of the push rod and the closed end of the axial bore in the plunger, said first compression spring means being adapted to resiliently urge the push rod to move outwardly from the housing bore through said push rod opening;

stop means adapted to prevent the push rod from moving completely out of the axial bore in the plunger, said stop means comprising a radially extending pin mounted on the inner end of the push rod that fits into a longitudinal slot formed in the interior surface of the axial bore in the plunger;

an annular locking member slidably mounted on said push rod within the axial housing bore between the inner end of the plunger and the push rod opening in the housing, said locking member being positioned for movable engagement with the plunger as the plunger moves toward said push rod opening, said locking member further comprising locking fingers that face said push rod opening, said locking fingers being radially movable with respect to wedging means adapted to prevent further axial movement of the locking member and move the locking fingers from their unlocked to their locked positions when the locking member reaches a predetermined point in the housing bore as it is moved toward said push rod opening, said wedging means comprising a conical surface formed adjacent said push rod opening, with the conical surface being mateable with the conical surface formed on the locking member; and

hydraulic drive means for selectively reciprocating the plunger along the housing bore from an unlocked position, wherein the locking fingers of the locking member are disengaged from the conical surface of the wedging means and are in an unlocked position, to a locked position, wherein the locking fingers of the locking member are wedged against the conical surface of the wedging means and are moved to their locked positions. 

1. A mechanical resistance locking mechanism comprIsing: a housing having an axial housing bore extending therethrough, said housing bore having a push rod opening at one end of the housing and a plunger opening at the other end of the housing; a plunger mounted for reciprocal movement within said housing bore, said plunger having an inner end inside the housing bore and an outer end outside the housing bore, with the plunger extending into the housing bore through said plunger opening; a push rod mounted for reciprocal movement with respect to said housing bore, said push rod having an inner end inside the housing bore and an outer end outside the housing bore, with the push rod extending into the housing bore through said push rod opening, said push rod further having a work contacting member on the outer end thereof; first resilient biasing means interconnecting the push rod and the plunger, said first resilient biasing means being adapted to resiliently urge the push rod to move outwardly from the housing bore through said push rod opening as the plunger is moved toward said push rod opening; a locking member carried by said push rod within said bore of said housing and axially slidable with respect to said housing bore and said push rod, said locking member being positioned for movable engagement with the plunger as the plunger moves toward said push rod opening, said locking member having locking fingers mounted thereon, which are radially movable with respect to said push rod from an unlocked position, wherein the locking fingers are disengaged from the push rod, to a locked position, wherein the locking fingers engage the push rod and prevent axial movement of the locking member along the push rod; wedging means adapted to move the locking fingers from their unlocked to their locked positions when the locking member reaches a predetermined point in the housing bore as it is moved toward said push rod opening; and means for selectively reciprocating the plunger along the housing bore from an unlocked position, wherein the locking fingers are in their unlocked positions, to a locked position wherein the locking fingers are in their locked positions.
 2. A mechanical resistance locking mechanism according to claim 1 and further comprising means for limiting movement of said push rod with respect to said plunger.
 3. A mechanical resistance locking mechanism according to claim 1 wherein said plunger moving means comprises a fluid cylinder having a piston rod fixed to the outer end of said plunger.
 4. A mechanical resistance locking mechanism according to claim 1 wherein movable engagement between the locking member and the plunger is effected by a second resilient biasing means interposed between the locking member and the plunger, said second resilient biasing means being adapted to resiliently urge the locking member toward said push rod opening as the plunger moves toward said push rod opening.
 5. A mechanical resistance locking mechanism according to claim 1 wherein: the inner end of the plunger has an axial bore therein that extends from said inner end to a closed end inside the plunger; the inner end of the push rod reciprocally fits within said axial bore; and said first resilient biasing means comprises a compression spring positioned in the axial bore between the push rod and the closed end of the axial bore.
 6. A mechanical resistance locking mechanism according to claim 5 and further comprising means for limiting the movement of said push rod with respect to said plunger.
 7. A mechanical resistance locking mechanism according to claim 6 wherein said limiting means comprises an axial slot in said plunger and a pin fixed to said push rod and extending into said slot.
 8. A mechanical resistance locking mechanism according to claim 1 wherein said plunger moving means comprises toggle clamp means including a handle for moving said plunger from said unlocked position to said locked position.
 9. A mechanical resistance locking mechanism aCcording to claim 8 wherein movable engagement between the locking member and the plunger is effected by a second resilient biasing means interposed between the locking member and the plunger, said second resilient biasing means adapted to resiliently urge the locking member toward said push rod opening as the plunger moves towards said push rod opening.
 10. A mechanical resistance locking mechanism according to claim 8 wherein said toggle clamp means comprises a handle link pivotably mounted to an outer end of said plunger, and a connecting link pivotably mounted at one end to said housing and at the other end to said handle link.
 11. A mechanical resistance locking mechanism according to claim 10 wherein the pivotable mountings of said connecting link and said handle link are aligned in a common plane when in locked and unlocked position.
 12. A mechanical resistance locking mechanism comprising: a housing having an axial housing bore extending therethrough, said housing bore having a push rod opening at one end of the housing and a plunger opening at the other end of the housing; a cylindrical plunger mounted for reciprocal movement within said housing bore, said plunger having an inner end inside the housing bore and an outer end outside the housing bore, said inner end having an axial bore therein that extends from said inner end to a closed end inside the plunger; a push rod extending from an inner end inside the housing bore through said push rod opening to a work contacting member on an outer end thereof, the inner end of said push rod extending into the axial bore in the plunger and being reciprocally movable with respect to aid housing bore and said plunger; a first compression spring means interposed between the inner end of the push rod and the closed end of the axial bore in the plunger, said first compression spring means being adapted to resiliently urge the push rod to move outwardly from the housing bore through said push rod opening; stop means adapted to prevent the push rod from moving completely out of the axial bore in the plunger, said stop means comprising a radially extending pin mounted on the inner end of the push rod that fits into a longitudinal slot formed in the interior surface of the axial bore in the plunger; an annular locking member slidably mounted on said push rod within the axial housing bore between the inner end of the plunger and the push rod opening in the housing, said locking member being positioned for movable engagement with the plunger as the plunger moves toward said push rod opening, said locking member further comprising locking fingers that face said push rod opening, said locking fingers being radially movable with respect to said push rod from an unlocked position, wherein the locking fingers are disengaged from the push rod and permit axial movement of the locking member along the push rod, to a locked position, wherein the locking fingers engage the push rod and prevent axial movement of the locking members along the push rod, said locking fingers have beveled outer surfaces thereof, such that the end of the locking member facing said push rod opening comprises a tapered conical surface; wedging means adapted to prevent further axial movement of the locking member and move the locking fingers from their unlocked to their locked positions when the locking member reaches a predetermined point in the housing bore as it is moved toward said push rod opening, said wedging means comprising a conical surface formed adjacent said push rod opening, with the conical surface being mateable with the conical surface formed on the locking member; and hydraulic drive means for selectively reciprocating the plunger along the housing bore from an unlocked position, wherein the locking fingers of the locking member are disengaged from the conical surface of the wedging means and are in an unlocked position, to a locked position, wherein the locking fingers of the locking member are wedged aGainst the conical surface of the wedging means and are moved to their locked positions. 